Refractory Bodies
It is known that a refractory body must possess the ability to stand up under exposure to high temperatures without undue chemical or physical change, to resist sudden changes in temperature without cracking or manifesting other evidence of body breakdown, to possess a relatively high mechanical strength at room temperatures and to maintain such strength at elevated temperatures, to resist various erosive and chemical, oxidative, and/or corrosive environments, and to possess a density and hardness suitable for the use to which the refractory body is to be put.
In order to obtain a high degree of perfection in respect to one or more of the above properties, it has usually been found necessary to forego the benefits of maximum performance in respect of certain other desirable properties. Thus, by way of example, the prior art has taught that, in order to obtain high-density beta-sialon compositions, one must use sintering aids which form a glass phase liquid at the sintering temperature. However, the use of such sintering aids tends to degrade the mechanical properties of the sintered product, often lowering the refractoriness. Thus, e.g., as is disclosed in P. Ferguson et al.'s "Sialons for Engineering and Refractory Applications" (Ceramic Engineering and Science Proceedings, Volume 6, No. 9-10, September-October, 1985, The American Ceramic Society, Westerville, Ohio), ". . . two major groups of Syalon ceramics are manufactured in which the intergranular phase composition is controlled by the variation in the level of additions in the starting mix. Materials can be formed with a microstructure containing beta-prime Syalon grains bonded a continuous, glassy second phase. The presence of the glassy phase limits the upper operating temperature range for such materials to around 800 degrees centigrade." (see page 1297)
Various refractory compositions especially suitable for one field of use are often found to be entirely unsatisfactory for other purposes. There is, thus, a continual demand for refractory bodies of new composition which will meet those demands of a special nature which require a combination of properties not to be found in those compositions of a refractory type already available.